The invention relates to a draft deflector for sliding roofs, removable roof sections or the like of motor vehicles which is formed by an airfoil profile which extends in the transverse direction of the vehicle, is arranged adjacent to a front edge of a roof opening, and can be moved from a sunk inoperative position into a swivelled-up operative position and vice versa, with the airfoil profile projecting beyond an imaginary roof contour at least in sections in the upward direction.
Draft deflectors of this type have the purpose of reducing annoying wind noise occurring during the drive and of preventing the air located in the vehicle interior from carrying out low-frequency vibrations which are disagreeable to vehicle occupants (sliding roof rumbling). These vibrations are caused by the fact that the air flow guided over the vehicle roof breaks off at the front transversely extending edge of the roof opening or at the draft deflector and, mainly at a low driving speed, does not surmount the roof opening but flows into the vehicle interior disposed below it. However, at the same time, because of the increased flow rate above the roof opening, a vacuum is generated in the vehicle interior which endeavors to take in air from there. Both currents result in annoying whirls which form in a periodically alternating manner. As a result, a pulsating of the air column takes place in the vehicle interior, which close to the natural frequency leads to considerable nuisance (noise, pressure in the ears).
A known arrangement of the initially mentioned type disclosed in German Patent Document DE-AS 23 39 680 has a draft deflector for a sliding roof which is arranged adjacent to the transversely extending front edge of the roof opening and is pivoted in a groove below the roof opening. The draft deflector which is formed by an airfoil profile can be moved from a sunk inoperative position upward into a swivelled-up operative position and vice versa. In the operative position, the draft deflector extends at a negative setting angle and projects slightly beyond the roof contour in the upward direction. It is a disadvantage of this arrangement that, as a result of the slight projection of the draft deflector in the operative position, depending on the length of the roof opening, it may occur that despite the swivelled-up draft deflector, the air current guided over the vehicle roof does not completely surmount the roof opening and flows into the vehicle interior located below which results in the unpleasant sliding roof rumbling. Because of the low-lying position of the airfoil profile, the current only flows against its top side and the air current is therefore deflected upwards, whereas the bottom side of the airfoil profile remains without any function.
From the German Patent Document DE-OS 23 39 679, a draft deflector for a sliding roof is known that is formed by an airfoil profile, is arranged approximately in the area of half the opening length of the sliding roof, and extends at a negative setting angle. The transversely extending draft deflector extends completely above an imaginary roof contour, a front edge of the draft deflector extending approximately at the level of the imaginary roof contour.
Because of the position of the airfoil profile, in this case also, the air current passing the top side of the vehicle interacts only with the top side of the airfoil profile, whereas no flow takes place around the underside of the airfoil profile. It may occur in the case of this draft deflector arrangement that a partial area of the air current breaks off before it reaches the draft deflector and flows into the vehicle interior located underneath, resulting in annoying vibrations (sliding roof rumbling) in the interior of the vehicle. Fluidically, the cross-sectional surface of the airfoil profile which increases in the flow direction has the effect that the flow against the airfoil profile does not take place with little resistance and that the air current breaks off or swirls behind the airfoil profile. The arrangement of the draft deflector approximately in the area of half the opening length of the roof would only be suitable to a limited extent for a removable roof section because the draft deflector would always have to be taken off before the roof section is removed.
It is an object of the invention to take such measures on a motor vehicle having a sliding roof, a removable roof or the like and a draft deflector that in the driving operation, when the roof is open, the occurring of annoying vibrations in the vehicle interior (sliding roof rumbling) is reliably avoided and the aerodynamic drag of the vehicle is affected only insignificantly.
According to the invention, this object is achieved by providing an arrangement wherein the airfoil profile is arranged such that in its swivelled-up operative position, the air current occurring as a result of the driving operation flows around the airfoil profile on both sides.
The principal advantages achieved by means of the invention are that, because of the fact that the current flows around the airfoil profile on both sides, the current, in a forced manner, is neatly guided away over the roof opening without the penetration of any partial air current into the vehicle interior. The occurrence of annoying sympathetic vibrations (sliding roof rumbling) is reliably prevented, the noise level in the vehicle interior is clearly lower, and the aerodynamic drag is essentially maintained.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.